Photochromic material, its method of manufacture, and products produced therefrom

ABSTRACT

A monomer which would normally be clear and transparent upon polymerization is co-deposited with silver halide particles of extremely small particle size onto transparent glass or plastic by plasma polymerization or glow discharge polymerization. The resultant coated glass or plastic material will exhibit photochromic behavior and may be used in the manufacture of eyeglasses, architectural glass, or glass for automobile windows or windshields.

BACKGROUND OF THE INVENTION

Reversible photochromic materials have found application primarily ineyeglasses and these are made of glass containing silver halideparticles with small additions of copper for improving the sensitivityof the system.

The main objection to eyeglasses made in this fashion is that they areheavier than plastic eyeglasses and need to be individually tested inaccordance with standard safety tests prior to sale. Because of cost,such photochromic glass has not found widespread application asarchitectural glass or as automobile window glass.

SUMMARY OF THE INVENTION

The instant invention involves co-depositing a monomer which wouldnormally be clear and transparent upon polymerization with silver halideparticles of extremely small particle size. Some of the monomers thatare satisfactory are hexamethyldisiloxane (HMDO), hexamethyldisilizane(HMDS), vinyl trimethylsilane (VTMS), tetramethyldisiloxane, and vinyltrimethoxysilane. These monomers when polymerized are also scratchresistant. Another material that meets the criteria of being clear andtransparent upon polymerization is aceto-nitrile which is not as scratchresistant. The particle size chosen is less than the wave length oflight and preferably the particles are from 25-150 angstrom (Å) indiameter and is controlled by the relative deposition rates of thesilver halide particles. While various silver halides may be used,silver chloride is the preferred material and HMDO and HMDS arepreferred monomers. Various sensitizers may be used with the silverhalides such as copper. The preferred co-deposition process is plasmapolymerization and the transparent glass or plastic substrates uponcoating have use as eyeglasses, architectural glass, and automobilewindow glass.

It is therefore an object of this invention to provide a coatingmaterial and its method of manufacture which exhibits reversiblephotochromic characteristics.

It is a further object of this invention to provide a method ofdepositing said material on a transparent substrate, either glass orplastic.

It is a still further object of this invention to provide such a coatedsubstrate which may be fabricated into an eyeglass, architectural glass,or automobile window glass.

Additional objectives and advantages of the present invention willbecome more readily apparent to those skilled in the art when thefollowing general statements and descriptions are considered.

DETAILED DESCRIPTION OF THE INVENTION

This invention involves the discovery that when silver halide particlesare entrained in a monomer which would normally be clear and transparentupon polymerization as a result of codepositing the monomer and thesilver halide particles on a substrate, the resultant product willexhibit photochromic properties and will darken appreciably and willrestrict the amount of visible light when the resultant product isexposed to light. When the light source is reduced, the resultantproduct will lighten permitting the increased transmission of visiblelight therethrough.

Silver halide in the particle size of 25 Å to 150 Å is preferred and thesilver halide must be of a size smaller than the wave length of light.The silver halide is dispersed in the polymer and the amount dispersedis 0.1-1.5 parts for 99.9-98.5 parts of polymer. The size of theparticles and the interparticle spacing are controlled by the relativedeposition rates.

The preferred deposition process is plasma polymerization which issometimes referred to as glow discharge polymerization. This is definedas the vapor phase reaction of low molecular weight organic materials asthe result of electron bombardment, ultraviolet radiation, or electricaldischarges to produce thin polymeric coatings on metallic or nonmetallicsubstrates. The polymerization takes place in a partial vacuum,typically between 10 and 10⁻² Pa (10⁻¹ and 10⁻⁴ torr). The substrate maymerely be immersed in the plasma and need not exhibit surface conductionbut rather can be allowed to float electrically relative to the plasmapotential. This enables the coating of unusually shaped substrates,large numbers of small substrates, or very large substrates. The silverhalide is supplied to the region where the substrate is located,typically utilizing the evaporation process.

The thus coated substrates may be used for eyeglasses, architecturalglass, and automobile window and windshield glass.

While this invention has been described in its preferred embodiment, itis to be appreciated variations therefrom may be made without departingfrom the true scope and spirit of the invention.

What is claimed is:
 1. A photochromic material containing particles ofsilver halide dispersed in a polymer which would otherwise be clear andtransparent said polymer being formed from a monomer selected from thegroup consisting of hexamethyldisiloxane (HMDO), hexamethyldisilizane(HMDS), vinyl trimethylsilane (VTMS), tetramethyldisiloxane, and vinyltrimethoxysilane, said silver halide particle size ranging from about 25Å to 150 Å and said silver halide being present from 0.05 percent to 1.5percent weight of the total coating material present.
 2. The coatingmaterial of claim 1 wherein said silver halide is silver chloride.